A school sports contain 68 students 33 do field events 40 do track events 23 do swimming 14 do both field and track events 8 do both swimming and field events if 15 students do field events only and 10 do both swimming and track events, how many students do swimming only
If you draw a Venn diagram, you can see that if x do all three, then
33+40+23 - (14+10+8) + x = 68
x = 4
so 23-(4+4+6) = 9 do swimming only